A video system can tolerate a relatively high pixel error rate without noticeably degrading the displayed video image. Pixel errors will manifest as sparkles that will be mostly un-noticeable in the displayed image.
However, video control errors may corrupt the entire displayed frame and may also corrupt the output audio. Thus, even a relatively small number of errors can result in noticeable image flickering and audible bursts of noise. Consequently, video control symbol errors must be prevented while video data symbol errors may be tolerated.
Most forward error correction schemes focus on protecting the entire data stream. This approach adds between 7% and 10% overhead to the data stream and requires logic that is large and complex.
In 64B/66B, prior art forward error control is inherently incapable of protecting sync bits, i.e. the prior art is unable to correct sync bits. While the prior art may be able to detect that a sync bit error occurred, it will not be able to determine how to correct the error. This failure will cause the entire 66B coded word to be lost or corrupted.
The disclosed invention provides effective protection for video control without introducing either the overhead or complexity associated with traditional forward error correction schemes.